Heat sufficient oil in a kadai.
Place a muslin cloth over a bowl. Put cabbage, carrot and salt on the cloth and set aside for 5 minutes so that they leave water. Gather the edges of the cloth and squeeze out excess water and transfer into another bowl. Reserve the water.
Add cornflour and refined flour to the vegetables and mix well. Divide the mixture into equal portions, shape into balls and coat with cornflour.

Gently slide in the balls into hot oil and deep-fry till golden brown and crisp. Drain on absorbent paper.
To make the sauce, heat 2 tbsps oil in a non-stick pan.
Roughly chop spring onion bulbs and reserve the greens.
Add the bulbs to the pan along with garlic, ginger, celery and green chillies to the pan. Add 1½ cups vegetable stock, reserved cabbage-carrot water, soy sauce, chilli sauce, salt and black pepper powder, mix well and bring to a boil.

Mix together 2 tbsps cornflour and ¼ cup vegetable stock in a bowl to make slurry. Add 2 tbsps slurry to the boiling sauce, mix well and cook for a minute or till the sauce thickens.
Switch off heat, add fried balls, vinegar, mix well and set aside for 5 minutes.
Diagonally slice the spring onion greens. Transfer the veg Manchurian into a serving bowl, garnish with spring onion greens and serve hot with fried rice or hakka noodles.